1. Field of the Invention
The present invention generally relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device having an optical sheet with an optical processing region.
2. Background Information
A conventional liquid crystal display device includes a rear frame, a linear light source, a pair of lamp frames, a liquid crystal cell, a plurality of optical sheets and a bezel. The rear frame is made of sheet metal. The linear light source includes a plurality of slender fluorescent tubes. The lamp frames covers and hides both longitudinal ends of the linear light source. The lamp frames are attached to the rear frame. The liquid crystal cell is attached to the rear frame. The optical sheets are interposed between the rear frame and the liquid crystal cell. The optical sheets include a light diffusing plate. The liquid crystal cell and the optical sheets are fixed to the rear frame by the bezel.
With the liquid crystal display device, the light diffusing plate diffuses light emitted from the linear light source. The light diffusing plate serves to make the brightness more uniform on a display face of the liquid crystal cell. Optical processing regions in the form of a plurality of bands extend from one end to the other end of the light diffusing plate. The optical processing regions are formed by printed regions on just one side of the light diffusing plate. The light diffusion ratio in the optical processing regions is varied in a width direction of the optical processing regions.
With the conventional liquid crystal display device, processing for forming the printed regions on one side of the light diffusing plate (hereinafter referred to as “print processing”) involves designating one side or one corner of the rectangular light diffusing plate as a reference position, and print processing positions are usually determined based on spacing calculated using the reference position as a starting point. Also, positioning of the light diffusing plate during the attachment of the light diffusing plate to the rear frame is carried out using an inner peripheral face of a peripheral wall of the rear frame as a reference.
However, the light diffusing plate is made of a plastic sheet or plate. Since the plate or sheet is thus made of plastic, temperature changes and other such thermal effects will cause the light diffusing plate to exhibit relatively large expansion and contraction. Therefore, the expansion and the contraction due to the thermal effects are taken into account, and the light diffusing plate is produced in a size that is slightly smaller than the rectangle inner face of the peripheral wall of the rear frame, so as to prevent deformation of the light diffusing plate.
Consequently, relatively large gaps inevitably end up being formed in longitudinal and lateral directions between the light diffusing plate and the inner peripheral face of the peripheral wall of the rear frame. As a result, the light diffusing plate becomes misaligned in the longitudinal direction (the width direction of the optical processing regions) and the lateral direction. Furthermore, the linear light source and the optical processing regions of the light diffusing plate deviate from correct positions. Moreover, variance tends to occur in the brightness of the display face of the liquid crystal cell. This problem is also caused by the effect of the nominal deviation found in each part.
Meanwhile, with another conventional liquid crystal display device, light from an edge lamp type of light source is emitted from a plane using a light guide plate, and the light is passed through an optical sheet (see Japanese Laid-Open Patent Application Publication No. H11-84351, for example). The conventional liquid crystal display prevents strain deformation of the optical sheet or prevents an offset of the optical sheet by increasing the optical sheet placement accuracy in the liquid crystal display device. Furthermore, with another conventional liquid crystal display device, the brightness of a backlight becomes uneven if an optical sheet disposed in a small gap between a liquid crystal panel and a light guide plate is deformed in an undulating shape by thermal expansion. The conventional liquid crystal display device is conceived to prevent such brightness unevenness (see Japanese Laid-Open Patent Application Publication No. 2003-43484, for example). Moreover, another conventional liquid crystal display device is conceived to prevent the leakage of light from a backlight (see Japanese Laid-Open Patent Application Publication No. 2007-10818, for example).
The above-mentioned Japanese Laid-Open Patent Application Publication Nos. H11-84351 and 2003-43484 suggest ways to increase the accuracy with which an optical sheet is attached in a liquid crystal display device. However, there is no mention at all of a positional relationship between the linear light source and the optical processing regions of the light diffusing plate included in the optical sheet, nor is there any discussion suggesting the positional relationship between these two.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved liquid crystal display device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.